Well, copyright owners can still send DMCA takedown requests on links that include the decryption key. But Mega can't automatically take down copies of the data (since any copies will be encrypted by a different key), and more importantly they can't offer big copyright houses custom tools (like MegaUpload did, and Youtube does) that find and flag material for them automatically.

It depends if he tries to monetize it by paying referral fees to websites indexing all the pirated stuff ... again.

Nobody cares about one to one piracy.

I wonder how much of a house of cards would be necessary to distance MEGA from such indexing sites and yet still profit from it. Dotcom did say he is interested in new business models. How new could it be?